Refining of fatty acids



Patented Get. 16, 1951 l'iED STATES PATENT OFFICE.

REFINING 0F FATTY. ACIDS Ward J. Bloomer, Westfield, N. J assignor toThe Lumrnus Company, New York, N. Y., a corporation of DelawareApplication April 26, 1946, Serial No. 665,083

3 Claims.

This invention relates to the refining of fatty acids and particularlyto an improved method of obtaining fractions of fatty acids havingdifferent characteristics. It is a continuation-in-part of my copendingapplication Serial No. 402,363, filed July 14, 1941, entitled SolventFractionation of Fatty Acids, which is now abandoned.

Mixtures of fatty acids are generally comprised of both saturated andunsaturated members in varying proportions. The several acids present,in such a mixture of higher fatty acids derived from a vegetable,animal, or synthetic source usually include palmitic, stearic, oleic,linoleic, and linolenic; Other acids, both saturated and unsaturated,may also be present, however.

Fatty acids find a use in the manufacture of many products. For example,the metallic salts of palmitic, stearic, and oleic acids, particularlythe sodium and potassium salts, form the various soaps. The unsaturatedacids may be used in the preparation of synthetic resins and plastics.These acids also have many other important applications.

The fatty acids, when esterified with glycerine, form the correspondingglycerides, which are valuable either as food products or as drying oilsaccording to the degree of saturation of the particular glyceride. Theglycerides of palmitic and stearic acids, both of which are saturated,are

valuable as edible oils and are non-drying in nature. Although oleicacid contains a single double bond and, hence is unsaturated, itsglyceride is also non-drying; this glyceride also finds use as an edibleoil. The glycerides of linoleic acid and of linolenic acid, whichrespectively contain two and three nonconjugate double bonds, are gooddrying oils because of the increased activity of the double bonds.Elaeo-stearic and licanic acid glycerides contain several double bondsin conjugate relationship, in which positionthe double bonds areextremely active, and are very fastdrying oils.

In order to take full advantage of the different individual propertiesof the various acids present, it is highly desirable to separate such amixture into fractions which are respectively relatively more saturatedand relatively more unsaturated in nature. Heretofore, such a separationhas been accomplished principally by distillation; but in this procedurethere are the disadvantages that decomposition of some of the fattyacids usually occurs at the high temperatures necessary even though thedistillation is effected under vacuum and that the fractionationaccomplished may. not be so sharp as desired. Thense of -sol-;

vents to effect a separation of the saturated from the unsaturated fattyacids by a liquid-liquid phase separation as well as by a liquid-solidphase separation has also been proposed. Attempts in this respect havenot been entirely satisfactory, however, because of certain operating orother disadvantages in each particular instance.

A specific object of my invention is to separate soybean fatty acidmixtures into fractions-comprising the relatively more saturated and therelatively more unsaturated constituentssothat the respective acids maybe moreadvantageously utilized.

Other objects and advantages of my invention will appear from thefollowing description thereof taken in connection with the accompanyingdrawing in which the single figure is-a diagrammatic flow sheet of aprocess embodying m invention.

In carrying out my invention, I bring the mixture of fatty acids and thesolvent into intimate contact to produce a solution of fattyacids. Thissolution is gradually cooled and chilled until the desired amount of therelatively more-saturated acids precipitates or separates out. Thisinsoluble material is then separated from the remaining liquid byfiltration or the like. The solvent retained in the filter cake and thefiltrate is suitably recovered as by distillation, and the separatedfatty acid fractions may then be utilized for their respective purposes.

In the following description reference is made to the solventfractionation of soybean fatty acids. Soybean fatty acids may be derivedfrom soybean oil, which in turn has been extracted from the soybean, bysplitting the oil, which consists of glycerides of the fatty acids, intoglycerine and the free fatty acids by hydrolysis in the presence ofsteam. For convenience, the approximate composition of soybean fattyacids is given below (see- Chemical engineering advances in soybeanprocessing by Gordon W. McBride in Chemical and MetallurgicalEngineering, vol. XLVII, No. 9 (September 1940), pp. 614, 618) As shown.in the accompanying drawing, the

, mixture of fatty acids. is introduced into the system at In. Inasmuchas these fatty acids will be substantially liquid at the usualatmospheric temperature, they can be readily pumped through line by pumpl I. A suitable solvent from line [2 is added to the fatty acids, andthe resulting mixture is thoroughly agitated in mixer I4 to insure thatthe fatty acids are completely dissolved in the solvent. If desirable ornecessary, the mixture of fatty acids and solvent may be slightly heatedin order to effect complete solution. In such case, mixer l4 may bedispensed with, and the mixture may be circulated through a heatexchanger (not shown), wherein the desired heat is provided and theturbulent flow insures complete solution.

In accordance with my invention, the solution of fatty acids is thenpassed through heat exchanger [6 wherein its temperature is considerablylowered. The cooled solution then flows through line [1 to chiller l8,through which ammonia is preferably circulated as by line l9 as theheat-removing medium in indirect contact with the solution. In chillerI8 the temperature of the solution is lowered sufiiciently toprecipitate out the portion of the fatty acids which it is desired toseparate from the original mixture.

The portion of the acids which separates out from the soybean fattyacids comprises the relatively more saturated fatty acids and consistsof palmitic and stearic acids as well as some oleic acid whereas thefatty acids remaining dissolved comprise oleic, linoleic, and linolenic.

The chilled mixture containing the precipitated fatty acids isaccumulated in surge tank 20,

from which it is continuously passed to rotary that used to form theinitial solution, serves to displace the greater portion of therelatively more unsaturated fatty acids which are retained in the filtercake. The wash solvent filtrate may be removed from the filter throughline 3| into receiver 32. The filter cake may be continuously removedfrom the filter surface as by a, scraper knife (not shown) and may bedischarged by screw conveyors 34 into hopper 35. This hopper ispreferably provided with a steam coil 36 or the like so that the filtercake may be melted down for convenient disposal.

It will be appreciated that the application of my invention is notlimited to the use of a rotary or other special type filter.Furthermore, either pressure or vacuum filtration may be used; thechoice of the particular system used will depend primarily on the amountof acids precipitated and on the efliciency of the washing step. It mayalso be found desirable to use a flue gas system (not shown) to blanketthe surge tank 20, wash solvent tank 29, filter 22, receivers 26 and 32,and hopper 35 in order to make the apparatus fireproof andexplosion-proof.

For recovery of the solvent, the filtrates collected in receivers 26 and32 may be combined, and the resulting mixture may be passed through Aline 38 as by pump 39 to exchanger l6 wherein it serves to lower thetemperature of the incomins solution of fatty acids.

The combined ill-- trate is then heated in heater 4!! to a temperatureabove the boiling point of the solvent and is introduced into the upperpart of distillation tower 4| wherein the greater portion of the solventis separated from the relatively more unsaturated fatty acids. Thisdistillation may be accomplished at atmospheric pressure or under vacuumproduced by vacuum pump 42 as desired. Dry solvent is removed overheadand is condensed in condenser 43. The net condensate is dischargedthrough line 44 into receiver 46, from which solvent is withdrawnthrough line 41 as by pump 48 and passed through line I2 to be mixedwith the incoming fatty acids in line In. The relatively moreunsaturated fatty acids are preferably introduced by means of trappedline into the lower part of distillation tower 4|, which may also beoperated under vacuum. Imperforate plate 50 serves to separate the twoparts of the tower from each other. Stripping steam may be introducedthrough line 51 to aid in the removal of the remainder of the solventfrom the unsaturated fatty acids, which may be removed as a bottomsproduct through line 52. The wet solvent vapors may be removed from thelower part of tower 4| through line 53 for introduction into a system(not shown) for dehydration of the solvent.

The melted filter cake of relatively more saturated fatty acids may bepumped through line 55 and heater 56 as by pump 51 and is introducedinto the upper part of distillation tower 58 for separation of thegreater portion of the solvent therefrom. This distillation may likewisebe carried out at atmospheric pressure or under vacuum produced byvacuum pump 42. Dry solvent is taken off overhead and condensed incondenser 60 the net condensate is discharged through line 6| intoreceiver 46. The relatively more saturated fatty acids are preferablyintroduced by means of trapped line 62 into the lower part of tower 58wherein the remaining solvent is separated therefrom. This part of thetower may also be operated under vacuum and is also separated from theupper part of the tower by imperforate plate 64. Stripping steam mayalso be introduced at 65 to aid in the removal of the remainder of thesolvent from the relatively more saturated fatty acids, which areremoved as a bottoms product through line 56. The wet solvent vapors maybe discharged through line 68 into the solvent dehydration system (notshown). It will be appreciated that, in place of heaters 40 and 56, heatexchangers utilizing steam as the heating medium may be employed.

Wash solvent is provided by withdrawing a portion of the solvent fromreceiver 46 and passing it through lines 41 and 10 as by pump 48 intotank 29, from which it is discharged through line 28 into filter 22 forwashing of the fatty acid filter cake. This wash solvent is preferablycooled in exchanger 'H by indirect contact with a cooling mediumcirculated through line 12.

In the solvent fractionation of soybean fatty acids, melting point 65F., iodine number (Wijs) 137.3, I have found that ethyl alcohol isparticularly eifective as a selective solvent. With a solvent ratio of3:1 and a wash ratio of 2:1 at a filtering temperature of -l0 F., 84.3%filtrate of unsaturated fatty acids having an iodine number of 157.4 anda pour point of 5 F., and 15.7% filter cake of saturated fatty acidshaving an iodine number of 8.2 and a melting point of 122 R, wereobtained in a single pass.

It will be appreciated that the ultimate yields and efiiciencies ofseparation will depend to a large extent on the solvent ratio (ratio ofsolvent to fatty acid feed) and the wash solvent ratio (ratio of washsolvent to fatty acid feed) used. In operating my improved process, Iprefer to use a solvent ratio of 3:1 although the range of solvent ratiomay extend from 0.5:1 to 6:1. The ratio of wash solvent is preferably2:1, but ratios ranging from 0.5:1 to 4:1 may also be used. The solventratio and the wash ratio used will depend primarily on the balance ofthe fatty acid separation obtained against the cost of recovery andrefrigeration of the solvent used. In addition, the solvent ratio usedwill depend on the concentration of saturated acids in the feed and thefiltering temperature.

I also find it desirable in some cases to recycle chilled filtratesolution, as by line 38a to the feed to increase the ratio of liquids tosolids to improve the liquid solid separation and provide a moreefficient cake thickness and more effective crystallization.

Although I have shown and described a preferred manner of carrying outmy invention, I am aware that modifications may be made thereto;therefore, only such limitations as appear in the claims appendedhereinafter should be applied.

I claim:

1. The method of resolving a mixture of the fatty acids derived from soybean oil into a fraction containing substantially only unsaturated acidsand a second fraction containing substantially only saturated acid whichcomprises feeding a mixture of the fatty acids having an iodine numberof approximately 137 (Wijs) to a mixing device and mixing said acidsWith non-toxic ethyl alcohol, reducing the temperature of said mixtureto below F., continuously filtering said mixture, washing the filtercake and separating as a filtrate approximately 85% of the charge asunsaturated acids having an iodine number in excess of 160 from theremainder of the charge as saturated acids having an iodine number lessthan 10.

2. A process for the separation of fractions of saturated acids fromfractions of unsaturated fatty acids in a mixture of soybean fatty acid,which comprises dissolving the mixture in 95% ethyl alcohol with asolvent ratio of three parts of alcohol to fatty acid, cooling thesolution to below 0 F. to efiect precipitation of the saturated acidfraction, making a liquid solid separation to separate the saturatedacid fraction from the remaining liquid containing the unsaturated acidfraction, separately recovering the solvent from said fractions andwashing said relatively saturated acid fraction with said recoveredsolvents, said wash ratio being at least 2:1 whereby a saturated fattyacid fraction of 8.2 iodine number and an unsaturated fatty acidfraction of 157.4 iodine number are recovered in one pass.

3. The method of making a fractional cut in the oleic acid range of asoya fatty acid to separate completely all higher unsaturated componentsfrom all saturated components, said acid having a general range of 13%saturated components and higher unsaturated components whereby a highyield of a product having an iodine number of nearly and the balance ofa product having an iodine number of less than 10 may be simultaneouslyobtained in a once through operation, which comprises mixing frombetween two and four parts of ethyl alcohol with the fatty acid attemperatures at which the mixture is fluid, thereafter sub-cooling saidmixture to a temperature in the range of from 20 F. to below 0 F.whereby saturated components of the mixture are precipitated,continuously filtering the precipitated constituents from the liquidunsaturated components and the solvent, Washing the cake formed withadditional solvent in the ratio of at least two parts of solvent to oneof cake to liberate any retained unsaturated component, heating thefilter cake to remove the solvent therefrom, separately heating thefiltrate to recover the solvent therein, returning such solvents forprimary use, and thereafter independently steam stripping the filtrateand filter cake to produce the desired end products and I wet solvent.

WARD J. BLOOMER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,045,727 Rider June 30, 19362,113,960 Grote et a1. Apr. 12, 1938 2,291,461 Freeman July 28, 19422,293,676 Myers et al. Aug. 18, 1942 2,340,104 Brown Jan. 25, 1944

1. THE METHOD OF RESOLVING A MIXTURE OF THE FATTY ACIDS DERIVED FROM SOYBEAN OIL INTO A FRACTION CONTAINING SUBSTANTIALLY ONLY UNSATURATED ACIDSAND A SECOND FRACTION CONTAINING SUBSTANTIALLY ONLY SATURATED ACIDSWHICH COMPRISES FEEDING A MIXTURE OF THE FATTY ACIDS HAVING AN IODINENUMBER OF APPROXIMATELY 137 (WIJS) TO A MIXING DEVICE AND MIXING SAIDACIDS WITH NON-TOXIC ETHYL ALCOHOL, REDUCING THE TEMPERATURE OF SAIDMIXTURE TO BELOW -10* F., CONTINUOUSLY FILTERING SAID MIXTURE, WASHINGTHE FILTER CAKE AND SEPARATING AS A FILTRATE APPROXIMATELY 85% OF THECHARGE AS UNSATURATED ACIDS HAVING AN IODINE NUMBER IN EXCESS OF 160FROM THE REMAINDER OF THE CHARGE AS SATURATED ACIDS HAVING AN IODINENUMBER LESS THAN 10.